1. Field of the Invention
The present invention is related to a radiation imaging apparatus which is capable of obtaining elongated images having dimensions greater than a detectable range of a radiation image detecting means thereof.
2. Description of the Related Art
Conventionally, various radiation detectors, for obtaining radiation images to be utilized for medical diagnoses and the like, have been proposed and are in practical use.
For example, there are radiation detectors that utilize semiconductors such as amorphous selenium that generate electrical charges when irradiated by radiation, as disclosed in U.S. Pat. No. 6,268,614. Radiation detectors of this type that employ the so called optical readout method and the TFT readout method have been proposed. If these radiation detectors are employed, image information obtained by imaging operations can be obtained as digital data. This improves compatibility with diagnostic assisting devices and the like that employ computers.
In addition, Japanese Unexamined Patent Publication No. 2005-270277 proposes a method for generating an elongated image having dimensions greater than the detectable range of a radiation detector. In this method, the radiation detector is moved in a direction along and parallel to a radiation detecting surface of the radiation detector, and a plurality of imaging operations are performed at different positions. A plurality of images which are obtained by each imaging operation are combined, to generate the elongated image.
Further, Japanese Unexamined Patent Publication No. 2008-023015 discloses a radiation imaging apparatus equipped with a laser emitting means. The laser emitting means is utilized to display a cruciform mark on the surface of the body of a subject, to accurately determine the portion of the subject to be imaged during radiation imaging.
In the case that an elongated image is obtained by imaging a plurality of portions of a subject by moving a radiation detector and then combining the obtained images, the time of imaging differs for each image. Therefore, there is a problem that it becomes difficult to combine the images appropriately if the subject moves between imaging operations.
In order to solve this problem, it is desirable to obtain the position of the subject's body at each imaging operation, and to adjust the combining positions of the images when they are combined, based on the obtained positions. However, if a separate means for obtaining the position of subjects is provided, the construction of a radiation imaging apparatus becomes complex, and the cost thereof will increase.
Accordingly, there is demand for a radiation imaging apparatus that can solve the above problem at low cost.
The present invention has been developed in view of the foregoing circumstances. It is an object of the present invention to provide a radiation imaging apparatus for performing elongated imaging at dimensions greater than a detectable range of a radiation image detecting means, in which the accuracy of combining positions of elongated images is improved at low cost.
A radiation imaging apparatus of the present invention is a radiation imaging apparatus that moves a radiation image detecting means that obtains images of subjects by receiving irradiation of radiation which has passed through the subject with respect to the subjects to obtain a plurality of images at different positions, and combines the plurality of obtained radiation images to obtain elongated images having greater dimensions than the detectable range of the radiation image detecting means, comprising:
a radiation source for irradiating radiation;
a laser source for emitting a laser beam;
displacement measuring means, for measuring distances to a measurement target by receiving the laser beam which is reflected by the measurement target;
the radiation image detecting means;
moving means, for moving the radiation image detecting means in a direction along and parallel to a radiation detecting surface of the radiation image detecting means;
image processing means, for generating the elongated images by combining the plurality of radiation images; and
control means, for controlling the laser source, the displacement measuring means, and the image processing means such that the laser source scans positions that correspond to the end portions of images in the movement direction of the radiation image detecting means in the direction perpendicular to the movement direction with the laser beam at each of a plurality of imaging operations, the displacement measuring means measures the positions of the end portions of the subjects in the scanning direction of the laser beam by receiving the laser beam which is reflected during the scanning, and the image processing means matches the combining positions of the radiation images such that the end portions of the subjects which are measured during each imaging operation are matched, to generate the elongated images.
Here, the “radiation image detecting means” may be a solid state detector that converts radiation to electric charges either directly or after converting the radiation to light, then outputs the electric charges to the exterior, to obtain image signals that represent radiation images of subjects.
The solid state detector may be of any of a variety of formats. Regarding a charge generating process for converting radiation to electrical charges, there are solid state detectors of a light conversion type, and solid state detectors of a direct conversion type, for example. A solid state detector of the light conversion type temporarily stores signal charges, obtained at a photoconductive layer by detecting fluorescence emitted by phosphors due to irradiation with radiation, in a charge accumulating section, then converts the accumulated charges to image signals (electrical signals) and outputs the image signals. The direct conversion type of solid state detector temporarily stores signal charges, generated within a photoconductive layer due to irradiation with radiation and collected by a charge collecting electrode, in a charge accumulating section, then converts the accumulated charges to electric signals and outputs the electric signals. Regarding a charge readout process for reading out the accumulated charges, there are an optical readout method and an electrical readout method. In the optical readout method, accumulated charges are read out by irradiating a solid state detector with readout light (electromagnetic waves for readout). In the electrical readout method, accumulated charges are read out by scanning TFT's (thin film transistors), a CCD (charge coupled device), or a CMOS (complementary metal oxide semiconductor) sensor, which are connected to a charge accumulating section. Further, the solid state detector may employ the improved direct conversion method disclosed in U.S. Pat. No. 6,268,614.
In the radiation imaging apparatus of the present invention, a configuration may be adopted, wherein:
the control means controls the radiation source, the laser source, the displacement measuring means, and the image processing means such that the laser source emits the laser beam toward the subjects at each of the plurality of imaging operations, the displacement measuring means measures the thickness of the subject by receiving the laser beam reflected by the subjects, and the radiation source adjusts the intensity of irradiated radiation during the imaging operations based on the thicknesses of the subjects, and/or the image processing means changes the contents of the image processes administered onto the radiation images.
Note that the measurement of the thicknesses of the subjects may be performed in the following manner. Because the distance from the laser source to an imaging stage of the apparatus is known (or measured when measuring the thickness of a subject), a subject may be caused to stand in front of the imaging stage, and the distance from the laser source to the subject may be measured. This measured distance may be subtracted from the aforementioned known distance, to measure the thickness of the subject.
According to the radiation imaging apparatus of the present invention, a laser source for displaying the cruciform mark, which the apparatus is already equipped with, is utilized to scan positions that correspond to the end portions of images in the movement direction of the radiation image detecting means in the direction perpendicular to the movement direction with the laser beam at each of a plurality of imaging operations, the positions of the end portions of the subjects in the scanning direction of the laser beam are measured by receiving the laser beam which is reflected during the scanning, and the image processing means matches the combining positions of the radiation images such that the end portions of the subjects which are measured during each imaging operation are matched, to generate the elongated images. Therefore, a low cost improvement of providing the displacement measuring means that measures distances to measurement targets by receiving laser beams reflected by the measurement targets enables improvement of the accuracy of combining positions for generating elongated images.
Note that the end portions of subjects can be detected by administering image analysis on the obtained radiation images. However, this configuration requires that the end portions of the subjects be pictured in the radiation images. In contrast, the present invention can improve the accuracy of the combining positions even in cases that the end portions of subjects are not pictured in the radiation images. Further, the necessity of image analysis is obviated, which enables processing times during combination of radiation images to be shortened.
A configuration may be adopted, wherein: the laser source emits the laser beam toward the subjects at each of the plurality of imaging operations, the displacement measuring means measures the thickness of the subject by receiving the laser beam reflected by the subjects, and the radiation source adjusts the intensity of irradiated radiation during the imaging operations based on the thicknesses of the subjects, and/or the image processing means changes the contents of the image processes (a contrast adjusting process and an outline emphasizing process, for example) administered onto the radiation images. In this case, it becomes possible to obtain elongated images having higher image quality.